retrieve tf transform

edit

Hellow,

I'm trying to obtain information from the a tf transform. I've loaded my URDF file in the parameter server and run robot and joint state publish. Here is a picture of some links :

So I can see that the transform between /base_link and /camera is publish.

Now here is my code which is very simple as it is a test :

#include <ros/ros.h>
#include <tf/transform_listener.h>

int main(int argc, char** argv){
ros::init(argc, argv, "my_tf_listener");

ros::NodeHandle node;
tf::TransformListener listener(ros::Duration(10));



tf::StampedTransform transform;
try{
    geometry_msgs::PointStamped base_point;

    listener.lookupTransform("/camera", "/base_link", ros::Time(0), transform);
}
catch(tf::TransformException& ex){
    ROS_ERROR("Received an exception trying to transform a point from \"camera\" to \"base_link\": %s", ex.what());
}

};

I'm just trying to have the transformation between /camera and /base_link. But I run in that error :

 rosrun tobot_goal listen 
[ERROR] [1396346328.110845542]: Received an exception trying to transform a point from "camera" to "base_link": Frame id /camera does not exist! Frames (1):

which would tend to mean that /camera is not publish. And if I try with any other frame I have, the result is the same...

Why can't I seem to not access those transformations ?

Thanks a lot !